Genghis Khan
Honour Guards perform during a ceremony marking National Pride Day in front of the statue of Genghis Khan at Genghis Square, formerly Sukhbaatar Square, in Ulan Bator, Mongolia's capital.Reuters

Genghis Khan, known for his expansionist empire spanning several countries across Asia in the early 13th century, may have risen to power because of good climate, a new study says.

The history of climate was found latent in ancient trees growing in the Khangai mountains of central Mongolia, which was investigated by a team of researchers led by Neil Pederson of Columbia University.

The scientists, who were studying Mongolian wildfires, stumbled upon a variety of stunted Siberian pines in the remote mountains of Mongolia, which grew on lava formations left behind by earlier volcanic eruptions.

Some of the trees studied in the university's Lamont-Doherty Earth Observatory were more than 1,100 years old, while one piece of wood dated back to about 650 BC.

The rings of the knobbly trees showed that the early decades of 1200s, when Genghis Khan first rose to power, were marked by a sustained period of warmth and regular rainfall, something unusual in Mongolia which is generally known for its cold and arid climate.

Researchers say that the optimal climatic conditions increased the productivity of the grasslands, providing ample food for the livestock, a major source of wealth in those times.

Severe drought

Genghis Khan's rule was preceded by a severe drought between 1180 and 1190, but his regime saw good times of pleasant weather.

The theory goes that in the period marked by bad weather, the tribes were fragmented and busy fighting each other, but the decent climate of later years helped Genghis Khan to unite the warring tribes into a unified military that voraciously conquered neighbouring regions.

Riding on the bounty afforded by benign seasons, each of the soldiers of his army had many horses and had large herds of livestock, which permitted them to conquer vast areas comprising present-day countries of Korea, China, Russia, India, southeast Asia, the Middle East and Eastern Europe.

"The transition from extreme drought to extreme moisture right then strongly suggests that climate played a role in human events," Amy Hessl, co-researcher from West Virginia University told AFP.

"It wasn't the only thing, but it must have created the ideal conditions for a charismatic leader to emerge out of the chaos, develop an army and concentrate power.

"Where it's arid, unusual moisture creates unusual plant productivity, and that translates into horsepower. Genghis was literally able to ride that wave."